High-pressure metal-vapor discharge lamp

ABSTRACT

A high-pressure metal-vapor discharge lamp is formed by enclosing scandium-halide, preferably scandium-iodide (ScI3) in the amount of 1.80 X 10 7 to 9.27 X 10 6 gram mol/cc of confined gas, and at least 3.1 times said halide quantity in atomic ratio of free (metal) scandium, together with some mercury as a buffer gas, inside a translucent alumina tube. Such discharge lamp can maintain a luminous efficiency of over 70 lumen/Watt and a general color-rendering index of over 70 for a period in excess of 6,000 hours, and thus, it is very useful as a general lighting source.

United States Patent 1191 'Akutsu et al. Oct. 7, 1975 [54] HIGH-PRESSURE METAL-VAPOR 3,398,312 8/1968 Edris et a] 313/229 X LAMP 3,407,327 3/1968 Koury et al. 313/225 X I 3,586,898 6/1971 Speros et al. 313 229 [75] Inventors: Hrdez Akutsu, shlya; Ha u 3,772,557 11 1973 Yoshida et al 313 229 Yamazaki, Moriyama; Katsuaki lwama, Sakai; Naoki Saito, Takatsuki, all of Japan Appl. No.: 440,536

Primary ExaminerPalmer C. Demeo Attorney, Agent, or FirmWenderoth, Lind & Ponack [5 7 ABSTRACT A high-pressure metal-vapor discharge lamp is formed by enclosing scandium-halidc, preferably scandiumiodide (S01 in the amount of 1.80 X 10 to 9.27 X 10" gram mol/cc of confined gas, and at least 3.1

52 us. c1. 313/184; 313/221; 313/225; times said halide q y in atomic ratio of free 313/229 (metal) scandium, together with some mercury as a 51 int. (:1. [-1011 61/18; H01J 61/30 buffer g inside a translucent alumina tube. Such dis- [58] Field of Search 313/184, 225,229,221 charge p can maintain a ous e iciency of over 70 lumen/Watt and a general color-rendering [56] References Cit d index of over 70for a period in excess of 6,000 hours, UNITED STATES PATENTS and thus, it is very useful as a general lighting source.

3,351,798 11/ 1967 Bauer 313/229 X 7 Claims, 2 Drawing Figures 1,1 I, I I I 3' 3' l/l I 11/, 1 1/11 x I 1, r xl ll] 2 '3 l4 3 I I '1, 1", 1'1 I'l /1'. I l 11'11'1' l l l l l l l l ll US. Patent Oct. 7,1975

GENERAL COLOR- RENDERING INDEX PERFORMANCE, HOURS HIGH-PRESSURE METAL-VAPOR DISCHARGE LAMP BACKGROUND OF THE INVENTION This invention relates to a high-pressure metal-vapor discharge lamp, wherein a translucent alumina tube enclose therein scandium-halide and free scandium as luminous substances, together with a buffer gas and a starting rare-gas, and which is advantageous as a light source.

ln recent years, translucent alumina tubes have been used for enclosing alkali-metal vapor of high temperature and high pressure. For instance, a high-pressure sodium-vapor lamp which generates light by discharge in a high-pressure sodium vapor has already been realized by means of such tube. Such high-pressure sodium-vapor lamp is capable of emitting yellowish white luminescence of continuous spectrum ranging all over the visible area by making the sodium vapor pressure in the bulb 100 to 200 Torr., and its color rendering is tremendously improved as compared with the low-pressure sodium-vapor lamp of the prior art which were characterized by having the yellow luminescence rendered chiefly by sodium-D line spectrum. Though improved, however, said high-pressure sodium-vapor lamp has a color temperature of about 2,lOOl( and a general color-rendering index of about 30, and its color rendering is not quite sufficient for general lighting purposes.

Therefore, with a view to improving such color-rendering, there have appeared high-pressure discharge lamps enclosing metal halides as luminous substances in addition to said sodium, for instance, halides of such metals as indium, thallium, tin, scandium or dysprosium. However, when such metal halides are subjected to high temperature and high pressure inside the lamp bulbs, metalconstituents of such metal halides, which are enclosed in the high-pressure discharge lamps, tend to react and combine with some substances in the bulb walls. As a result, such high-pressure discharge lamps =-"are vulnerable to shortcomings that with long use, the

luminous color changes and the increase" of separated halogen in the bulb causes poor starting and sudden extinction of light, thus hampering their popularization as general lighting sources.

SUMMARY OF THE INVENTION The object of this invention is to offer a high-pressure metal-vapor discharge lamp having long life and stable discharge characteristics with a high color-rendering BRIEF EXPLANATION OF THE DRAWING FIG. 1 is a sectional side view of the discharge lamp embodying this invention.

FIG. 2 shows typical examples of lighting performance characteristics of said discharge lamp.

DETAILED DESCRIPTION OF THE INVENTION The discharge lamp of this invention comprises a translucent alumina tube as its luminous bulb, which encloses mercury as a buffer gas, rare gas, for instance,

2 xenon as a starting gas, and also scandium-halide, more preferably scandium-iodide, as a luminous substances.

The present inventors discovered that a high-pressure metal-vapor discharge lamp enclosing, in its translucent alumina tube, scandium-halide in the amount of 1.8 X 10 to 9.27 X 10' gram molecules/cc of inside volume of the tube and at least 3.1 times said scandium-halide quantity in atomic ratio of free scandium would fully perform the above-mentioned object.

The high-pressure metal-vapor discharge lamp of this invention is constructed in such a way that discharge electrodes are enclosed at both ends of the translucent alumina tube, inside which is enclosed mercury as a buffer gas so as to maintain a pressure between 2 and 10 atm. (atmosphere) all the time when the lamp is on.

Together with the mercury, starting rare gas, for instance xenon, is enclosed in the tube to a pressure of about 20 Torr. at room temperature at the time of enclosing. The xenon can be replaced by one of other known rare gases, for instance, neon, argon, etc.

Among scandium-halides as luminous substances, scandium-iodide is the most suitable, but bromides and chlorides can also be employed.

For further improvement in the color rendering of the lamp under this invention, it is efi'ective to enclose an appropriate quantity of halide of at least one element selected from alkali-metal group (Na, Li, Cs), titanium group (Ti, Zr), vanadium group (V, Nb) and rare earth group (Dy, La, Tm, Sm, Ho, Th, Hf) as luminous substance in addition to specified quantities of said scandium-halide and free scandium.

Detailed description by the embodiment of the highpressure metal-vapor discharge lamp of this invention will be made in the following.

FIG. .1 is a-sectional-side view of the discharge lam embodying this invention, wherein, at both ends of. a translucent alumina tube 1, niobium tubes 2 and 3 for electrode-leading-in, respectively, are airtightly sealed in, and said tube encloses stuffing composed mainly of scandium-iodide(ScI and free scandium(Sc). The alumina tube 1 is selected to have an inner diameter of between 15 and 20 mm and an inside volume of between .l2.4 and 22 cc. The surfaces of the electrodeleading-in niobium tubes 2 and 3 inside the tube 1 are airtightly bonded by a known halogen-resisting cement, and tungsten coils are used .for discharge electrodes. 4 and 5 whose mutual distance (namely, arc length) 1a is designed to be 50 mm.

For the purpose of systematically scanning the characteristics of discharge lamps, a number of lamps were prepared, which were uniform in that, each one had an alumina tube 1 with 15 mm inner diameter and 15 cc volume and enclosing therein 30 mg of mercury and 20 Torr. (at room-temperature) of xenon. However, varied selected quantities of scandium iodide(ScI and free scandium(Sc), varying in quantities from 0.5 to mg and from 0 to 40 mg, respectively, were added to the respective tubes. Then such lamps were respectively lit under the specified condition of standard for 400 W and their discharge characteristics were examined. As a result, the following facts were revealed:

1. When the additive quantity of Scl was increased,

a red colored luminescence increased, but on the otherhand, re-ignition voltage (namely, a minimum voltage capable of re-igniting the lamp right after extinction) rose, and along with the increase of Sel --extinction phenomena (namely, unexpected 's'udden extinction during a lighting) tended 3 to become frequent, even during short performance periods. 1

2. When an additive quantity of 'free' Sc was increased, such discharge lamp tended to maintain the desirable original characteristic for a longuse time. The above-mentioned first result, namely, increasing red colored luminescence, indicates that, with the increase of S01 the luminous spectrum strength of Sc increases, and therefore, the radiation component in the red color area increases to display high color-rendering as a light source. On the other hand, the high temperature and high vapor pressure of the lit lamp causes the scandium metal of the Scl in the tube 1 to react with the alumina component of the tube 1 and to reduce the Sc component. The diminishing Sc components corresponds to the dwindling phenomenon of the Sc spectrum strength in the lighting characteristic during burning, and also concurs with the fact that along with the diminishing Sc components, separated iodine in the tube increases and the re-ignition voltage gradually increases. Also by precisely examining the reaction between alumina and Sc, it is highly obvious that with increasing additive quantity of 801,, its reacting rate increases, and it is presumed that the higher the Sc vapor pressure gets, the higher the reacting rate becomes.

On the other hand, the above-mentioned second characteristic, namely, long maintenance of the initial characteristics, indicates that the added Sc reacts with the iodine separated during the burning and functions to keep the Scl vapor pressure in the tube constant. The vapor pressure of free Sc is considerably lower than that of SCI;,, and therefore, the Sc existing in free state in the tube hardly evaporates by itself. However, since Sc easily reacts with iodine gas at high temperatures, the existence of excessive quantity of free Sc works tokeep constant the S01 vapor pressure in the discharge tube, and at the same time, to prevent the emergence of free iodine in the tube.

In view of the above-mentioned facts, in order to obt'ain a discharge lamp having a sufficiently good performance for practical use, it is necessary to determine accurately the maximum and minimum additive quantities of S01 and free Sc, respectively. According to empirical studies conducted by the present inventors, each additive quantity should be 1.80 X 10 to 9.27 X 10* gram molecules per 1 cubic centimeter of inside volume of the bulb for S01 and at least 3.1 times said Scl quantity in atomic ratio (namely, at least 5.58 X 10 to 2.98 X 10 gram-atoms) for free Sc.

If the additive quantity of Scl is below said minimum (1.80 X gr. mol.), the spectrum radiation of Sc is insufficient to improve the color rendering, and the general color rendering index is always below 55, which is not sufficient for use as a general lighting source. On the other hand, if the additive quantity of S01 exceeds said maximum (9.27 X 10 gr. mol.), the corrosion of the electrode by iodine is heavy, shortening the life of discharge lamp.

When the additive quantity of free Sc was below 3.1 times that of Scl in atom ratio, the lamp showed an attenuation of radiation spectrum of Sc in a relatively short period, for instance, less than 500 hours. On the contrary, in case of over 3.1 times, the radiation spectrum of Sc did not attenuate even for over'3,000 hours. Consequently, it was empirically concluded that said value of 3.1 times was a critical value to the spectrum characteristic. The reason thereof can be induced as follows: In the vapor pressure value of Sc during the lit time, the equilibrium state between the solid-state Sc reacted with alumina of the tube wall and the vaporstate Se in the discharge tube is attained at about 500 hours after the lighting of the lamp. At this stage, the quantity of said reacted Sc corresponds to 3.1 times that of Se within Scl in atomic ratio, and after the attainment of the equilibrium state, the quantity of free Sc to be lost by reaction with the alumina markedly decreases.

According to intensive experiments of the inventors, a discharge lamp capable of maintaining such high efficiency and high color-rendering lamp-characteristics as luminous efficiency of over lm/W and general colorrendering index of over 70 for a period exceeding 6,000 hours was realized, by specially selecting the amount of the additive quantities of Sel to be in the range of 5.4 X 10 to 4.6 X 10 gram molecules per cubic centimeter of the inside volume of the bulb, and of free Sc to be at least 4.2 times that of Sel in atomic ratio.

As Example 1, a lamp of the same type as the abovementioned one, having an inner diameter of 15 mm, inside volume of 15 cc and distance between the electrodes of 50 mm, and filled with mercury: 30 mg, S01 6.8 mg, Sc: 10 mg and xenon: 20 Torr (at room temperature), maintained the above-mentioned lamp characteristics (luminous efficiency over 70 lm/W, General Color Rendering Index over 70) for 10,000 hours. This lamp also displayed such an excellent performance that almost no change in the luminous color was observed. In this case, the addition of 10 mg of free Sc corresponds to the addition of about 14 times said 6.8 mg. of Scl in atomic ratio.

Even if the addition of Sc in the quantity of over 30 times said 6.8 mg in atomic ratio of Sel were made, no improvement in the effect would be obtained, but rather, free metal would cause shadow only to deteriorate the luminous effect.

The color rendering of the discharge lamp of this invention can be further improved by adding other metal halides together with the above-mentioned S01 and Sc enclosed in the tube. In such case, however, metal halide additives that can be added shall be limited to those which resist reduction by aluminum vaporing from the wall of alumina tube during burning. For this reason, thallium iodide(TlI), indium iodide (lnl Tin iodide (Snl etc., used inside the conventional fused quartz tube of metal-halide lamp, cannot be added. The strength of the spectrum radiating from such metal halides attenuates during burning and causes the luminous color of the lamp to shift. Based on such facts, the present inventors researched for metal halide additives and found that metal halide additives of the alkali group, titanium group, niobium group and the rare earth group were suitable.

To describe concrete data of further Examples of discharge lamps of 400 Watt standard, alumina tubes having inner diameters of 15 mm and inside volume of 15 TABLE 1 Lamp Metal halide additive(s) Initial lamp characteristics No. (amount in mg) General color- Lamp efrendering ficiency index (lm/W) l Nal l-20) 75 70 2 Lil (lO-ZO) 74 67 3 Til (10-20) -79 65 4 Zrl, 10-20) 78 65 5 Nbl (IO-20) 72 7O 6 Hol,,( 5-l5) 75 67 7 Dyl;,( 5-l5) 73 68 8 Tml 5-15) 74 69 Thl. 3-20) 75 69 9 3' l0 Nal 10-20) Til lO-) 83 66 l l Nal lO-ZO) Z11 (10-20) 82 67 i2 Nal (l020) Nbl (IO-20) 78 69 13 Nal (10-20) Sml (l0-20) 78 70 I4 Nal (IO-20) Dyl (10-20) 78 70 i5 Nal (IO-20) Tml; (10-20) 79 69 16 Na] (IO-20) H0]; (10-20) 80 68 I7 Nal (IO-20) Lil (IO-20) 79 69 I8 Nal( l02O)+Til lO-ZQ )+Lil( lO-20) 88 63 I9 Nal( lO2O )+Til 10-20 )+Dyl;,( 5-l5) 84 65 mg figures in parentheses indicate suitable ranges for the lamps. Lamp No. l 9 additive of single kind added.

Lamp No. l0 l7: additives of two kinds added,

Lamp No. l8 l9: additives of three kinds added.

From the foregoing measurements, the following conclusions were drawn:

1. Whereas a lamp having only 6.5 mg of Scl and 2.9 mg of free Sc has a general color-rendering index of about 70, this index value is improved to 72 to 88 by further adding metal halide additives shown in Table 1.

2. Addition of alkali-group metal-halide additives is desirable, because it provides advantages of stabilizing the arcs in the luminous tube and lowering the re-ignition voltage, besides improving the color rendering. Sodium iodide (Na I) is most desirable when the efficiency is also considered.

3. The spectrum from titanium metal halides just covers the wave-length area not covered by the spectrum radiation from Sel and therefore, it is remarkably effective for improving the color render- As has been above-mentioned, for halides as enclosures inside the discharge lamp of this invention, iodides are the most desirable, but other halides with the exception of fluorides, namely, bromides and chlorides, are usable. In such cases, too, the life of such discharge lamps is by far longer as compared with the conventional discharge lamps enclosing reasonable amount of scandium-halide. Out of all such halides, the iodides have the least corrosive reaction and wearing of metal electrodes.

In case fused quartz glass is used for the bulb, free Sc metal disappears by sharp reaction with quartz under high temperature and quickly blackens the tubes. Hence, such lamps cannot give the desired discharge characteristics.

In FIG. 2, the performance characteristic of the discharge lamp of the Example I of this invention is shown by a curve I, and in contrast thereto, a characteristic example of a discharge lamp entirely without free Sc enclosed is shown by a curve ll. From this comparison,

What is claimed is: 1. In a high-pressure metal-vapor discharge lamp having a bulb made of a translucent alumina tube and enclosing buffer gas, luminous substances and starting rare-gas, the improvement which comprises said luminous substances being a mixture comprised of a scandium halide selected from the group consisting of scandium iodide, scandium bromide and scandium chloride in the amount of 1.80 X 10 to 9.27 X 10 gram molecules per 1 cubic centimeter of the inside volume of the bulb. and free scandium in the amount of at least 3.1 times said amount of scandium halide in atomic ratio.

2. A discharge lamp of claim 1, wherein the scandium halide is scandium iodide.

3. A discharge lampof claim 1, wherein the scandium halide is scandium bromide.

4. A discharge lamp of claim 1, wherein the scandium halide is scandium chloride.

5. A discharge lamp as recited in claim 1 wherein the specific proportions of the amounts are 5.4 X 10 to 4.6 X 10" gram molecules per cubic centimeter of the inner volume of the bulb for scandium halide and at least 4.2 times said amount of scandium halide in atomic ratio for free metal-scandium.

6. A high-pressure metal-vapor discharge lamp having a bulb of translucent alumina tube enclosing buffer gas, luminous substances and starting rare-gas, said luminous substances comprising the following components: scandium halide in the amount of 1.80 X 10' to 9.27 X 10 gram molecules per cubic centimeter of the inner volume of the bulb; free metal-scandium in the amount of at least 3.1 times said amount of scandium halide in atomic ratio; and an appropriate amount of halide of at least one element selected from the group consisting of alkali-metal group, titanium group, panagium group and rare-earth group.

7. A discharge lamp of claim 6, wherein the halide is it is evident that the discharge lamp of this invention iodine.

has a distinctly longer life than the conventional ones.

* ii l 

1. In a high-pressure metal-vapor discharge lamp having a bulb made of a translucent alumina tube and enclosing buffer gas, luminous substances and starting rare-gas, the improvement which comprises said luminous substances being a mixture comprised of a scandium halide selected from the group consisting of scandium iodide, scandium bromide and scandium chloride in the amount of 1.80 X 10 7 to 9.27 X 10 6 gram molecules per 1 cubic centimeter of the inside volume of the bulb, and free scandium in the amount of at least 3.1 times said amount of scandium haliDe in atomic ratio.
 2. A discharge lamp of claim 1, wherein the scandium halide is scandium iodide.
 3. A discharge lamp of claim 1, wherein the scandium halide is scandium bromide.
 4. A discharge lamp of claim 1, wherein the scandium halide is scandium chloride.
 5. A discharge lamp as recited in claim 1 wherein the specific proportions of the amounts are 5.4 X 10 7 to 4.6 X 10 6 gram molecules per cubic centimeter of the inner volume of the bulb for scandium halide and at least 4.2 times said amount of scandium halide in atomic ratio for free metal-scandium.
 6. A high-pressure metal-vapor discharge lamp having a bulb of translucent alumina tube enclosing buffer gas, luminous substances and starting rare-gas, said luminous substances comprising the following components: scandium halide in the amount of 1.80 X 10 7 to 9.27 X 10 6 gram molecules per cubic centimeter of the inner volume of the bulb; free metal-scandium in the amount of at least 3.1 times said amount of scandium halide in atomic ratio; and an appropriate amount of halide of at least one element selected from the group consisting of alkali-metal group, titanium group, panagium group and rare-earth group.
 7. A discharge lamp of claim 6, wherein the halide is iodine. 